Gastric emptying and secretion, as well as intragastric volume and composition, were determined simultaneously in three patients with Zollinger-Ellison syndrome and in seven normal subjects. Gastric hypersecretion was observed in patients with Zollinger-Ellison syndrome and in normal subjects receiving pentagastrin. In contrast, the fraction of gastric contents emptied per minute (fractional rate of emptying) was increased in Zollinger-Ellison patients and unchanged or decreased in normal subjects receiving pentagastrin. The increased fractional rate of gastric emptying in patients with Zollinger-Ellison syndrome persisted despite abolition of gastric hypersecretion by metiamide. Thus, the increased fractional gastric emptying seen in patients with Zollinger-Ellison syndrome is not attributable to hypergastrinemia, or to gastric hypersecretion per se. Instead, it appears to be caused by an undefined nervous or humoral factor.